METHOD FOR MANUFACTURING A STATOR FOR A ROTATING ELECTRIC MACHINE

Abstract: In a method for manufacturing a stator for a rotating electric machine, for example an asynchronous machine, which stator comprises a stator core (21) and a tubular housing (1) which at the operating temperature of the machine surrounds the stator core with a shrinkage fit, the manufacture of the housing comprises the following steps. A number of extruded profiles (31, 32, 33, 34), each of which being defined by two edges (345, 346) and comprising a concave smooth limiting surface (341) located between said edges and formed by generatrices along an arc with a radius of curvature substantially corresponding to the external diameter of the stator core, are fixed in relation to each other such that their concave limiting surfaces form a tubular configuration with a predetermined internal diameter. The number and dimension of the profiles between said edges are chosen such that gaps (41, 42, 43, 44) are formed between at least some of their edges when they are fixed to said tubular configuration. Thereafter, the profiles are welded together along their edges into a tubular housing by means of weld joints (51), the width of which is adapted to fill up said gaps.

Description: Method for manufacturing a stator for a rotating electric machine TECHNICAL FIELD 5 -, The present invention relates to a method for manufacturing a stator for a rotating electric machine, for example an asyn- ■ chronous machine, the stator comprising a stator core, sub¬ stantially in the form of a hollow circular cylinder, and a 10 tubular housing which, at the operating temperature of the machine, surrounds the stator core with a shrinkage fit. BACKGROUND ART 15 Stators for electric machines of the intended kind have hitherto often been manufactured with, for example, housings cast in aluminium. Casting of such housings entails high tool costs, above all in the case of large machine diameters and, particularly when the housing is cast directly around the 20 stator core, results in several difficult technical problems such as thermal emission to surrounding machine components, tendencies to cracking of the casting, etc., which have to be solved. Because of the heat generation during the casting process, the stator windings of the machine can be mounted in 25 the stator core only after the casting of the housing. It is further known to manufacture tubular blanks, preferably of aluminium, for stator housings by means of extrusion. In that connection, the housing is given such internal dimen- 30 sions that, at the operating temperature of the machine, it makes contact with the stator core with a shrinkage fit which provides sufficient torque transmitting and heat transmitting < ■ capacity but, after heating, can be applied around the stator ^ core. If the temperature increase of the housing is limited 35 to a level which is not harmful for the other parts of the stator, this method of manufacture permits mounting of the stator windings of the machine in the stator core before the housing is applied, which is an advantage from the point of CONFIRMATION view of production technique. However, because of the manufacturing tolerances which are associated with extrusion of tubular blanks, the housing normally has to be machined internally to ensure, on the one hand, the necessary shrinkage fit and, on the other, that the heating of the housing when it is applied around the stator core can be limited to a level which is harmless to the other stator parts. Considerable demands are placed on the capacity of the machines which manufacture the extruded blanks, which renders the blanks expensive to manufacture. The blanks are also voluminous, which entails high transport costs in the event that they are manufactured at some other place than that where the stator in its entirety is manufactured. These latter disadvantages are, of course, accentuated with increasing stator diameter of the machines. From EP-B-0 048 213 it is known to manufacture a housing of two or more extruded profiles, which, at their edges extending in the axial direction of the machine, exhibit a hook-shaped bar and a slot corresponding to the bar. The housing is held together by a hook-shaped bar on one profile engaging into the slot on the adjacent profile. The necessary grip between the housing and the stator core appears to be achieved by the bar resiliently engaging into the slot such that the housing is thereby kept against the stator core by a spring force. Especially in machines with large stator diameters and/or in the event that it is desirable for reasons of production technique to manufacture the housing from more than two profiles, for example four or more, this design probably leads to dimensioning problems and at least requires a strong dimensioning of the hook-shaped bar to ensure a sufficient grip between the housing and the stator core. SUMMARY OF THE INVENTION The object of the invention is to provide a method for manufacturing a stator for a rotating electric machine, which method permits the stator windings of the machine to be mounted in the stator core before the housing of the stator is applied around the stator core, but which eliminates the operation involving internal machining of the housing as well as the above-mentioned problems associated with the manufac¬ ture of tubular blanks for housings and with housings compri¬ sing a plurality of resiliently composed profiles. According to the invention, this is achieved by fixing a number of extruded profiles, each of which being defined by two edges and comprising a concave smooth limiting surface with a radius of curvature substantially corresponding to the external diameter of the stator core, in relation to each other such that their concave limiting surfaces form a tubular configuration with a predetermined internal diameter, the number and dimension of the profiles between the edges mentioned being so chosen that, placed together around the stator core, they would essentially surround the stator core without overlapping each other and such that gaps are formed between at least some of the edges thereof when they are fixed to the tubular configuration mentioned, and by welding the profiles together along their edges into a tubular housing with weld joints whose widths are adapted to fill up the gaps mentioned. Advantageous improvements of the invention will become clear from the following description and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail by description of embodiments with reference to the accompanying drawings wherein Figure 1A shows in cross section a stator core manufactured according to the invention, Figure IB shows a detailed enlargement of Figure 1A, Figure 2 shows a stator core on which a housing accor¬ ding to Figure 1A is to be applied, Figure 3A shows one of the profiles from which the housing according to Figure 1A is composed, Figure 3B shows a detailed enlargement of Figure 3A, and . Figure 4 shows a device for manufacturing a housing according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1A shows in cross section a tubular housing 1 for a stator for an electric asynchronous machine. The housing is intended to surround a stator core 21, schematically shown in Figure 2. The stator core substantially has the shape of a hollow circular cylinder with a known external diameter Dl. At the internal cylindrical limiting surface of the stator core, slots for the stator windings 22 of the machine are provided in a known manner (not shown in Figure 2) . These stator windings may be placed in their slots before the housing, manufactured according to the invention, is applied onto the stator core. The housing is composed of four identical extruded profiles 31, 32, 33, 34, of which profile 34 is shown in Figure 3A. The concave limiting surface 341 facing the stator core consists of a smooth surface, formed by generatrices along a circular arc whose centre in the figure is designated 0. The arc has a radius of curvature substantially corresponding to the external diameter of the stator core. The edges 345, 346 of the profile extend in the axial direction of the stator and the surface 341 exhibits, at each edge of the profile, recesses 3411, 3412 in a radial direction extending along the edges of the profile. In the direction of the arc, the extent of the profile comprises an angle of 90° less an arc length 2S, such that in relation to a symmetry line for the profile, at each edge of the concave surface, a play S is formed between the edge and a radius from 0 which forms an angle of 45° with the symmetry line. For a machine with the external diameter Dl of the stator = 200 mm, the play S may advan- tageously be chosen to be about 1 mm. The convex limiting surface 342, facing away from the stator core, exhibits a number of cooling ribs 3421 for improving the cooling of the . profile and the edges of the profile exhibit a bevel such that the gaps 41, 42, 43, 44 which are formed by the play S between two adjacently arranged profiles are wider at the convex limiting surface than at the concave one. In Figure 3A the bevel of the edges make an angle of 30° with the radial direction. Along their edges the profiles are joined into a tube by means of welds in the axial direction of the machine. Such a weld joint is shown in detail in Figure IB. The weld joint 51 fills up the gap 41 between the profiles 31 and 32. It is advantageous to arrange in the recess an axially extending supporting bar 61 for the weld. The supporting bar is of a material which during the welding fuses with the weld joint and is given such dimensions that the bar is completely accommodated in the space formed by the recesses on two adjacently located profiles. During the welding together of the profiles, these are fixed in relation to each other by being arranged, as shown in Figure 4, around an essentially cylindrical mandrel 7 with a predetermined diameter D2 in such a way that their concave limiting surfaces form a tubular configuration with an internal diameter corresponding to the external diameter of the mandrel. The mandrel comprises four jaws 71, 72, 73, 74 which in a manner known per se, but not shown in detail in the figure, are connected to each other. Each one of the jaws comprises in the tangential direction an arc of 90° less an arc length 2B. Profiles and jaws are placed in the tangential direction in such a way in relation to each other that one jaw supports adjacent parts of two adjoining profiles. Also in a manner known per se but not shown in detail in the figure, the jaws are essentially concentrically displaceable in a radial direction between two radial positions. The mandrel, with the jaws in their external radial position, is turned in a lathe into the desired predetermined diameter D2. The diameter of the mandrel is so chosen in relation to the external diameter Dl of the stator core that, on the one hand, the welded-together housing, which at room temperature will have the internal diameter D2, after heating to a temperature which is harmless for the other parts of the machine, for example 180°C, may be applied around the stator core but, on the other hand, at the operating temperature of the machine, makes contact with the stator core with a desired shrinkage fit. Further, the arc 2S is so chosen that gaps are formed between at least some of the edges of the profiles when they are fixed to the tubular configurations. To ensure good contact with the mandrel, the profiles are pressed against the mandrel with pistons 8 which make contact with a compressive force against support surfaces 317, 318, 327, 328, 337, 338, 347, 348 on the profiles. The compressive force is achieved, for example, by compressed air. The welding of the profiles then takes place by applying axially extending weld joints along the edges of the profiles whereby the weld joints automatically fill up the gaps which, when the profiles have been applied against the mandrel, are formed between adjacent profiles. Thus, the weld joints are given a width which gives the tubular housing the desired internal diameter and their width is automatically adapted to compensate for the width tolerances which have arisen during the extrusion of the profiles. The welding may advantageously be carried out by a welding robot (not shown in the figure) which is programmed for the purpose and which operates welding guns 9 along a predetermined track. When the welding is completed, the jaws are moved to their internal radial position, whereby the gaps existing between the jaws, when the jaws are located in their outer radial position, are reduced in width to adapt to the reduced circumference of the mandrel. Thereafter, the tubular housing can now be detached tively, be formed, for example, from a ceramic material which during the welding does not fuse with the weld joint, whereby the supporting bar in this case, after the welding, is removed and will not constitute part of the housing.

Claims: CLAIMS 1. A method for manufacturing a stator for a rotating electric machine, for example an asynchronous machine, said stator comprising a stator core (21) , substantially in the form of a hollow circular cylinder with a known external diameter, and a tubular housing (1) which at the operating temperature of the machine surrounds the stator core with a shrinkage fit, the stator core and the housing being manufactured as separate units, characterized in that the manufacture of the housing comprises the following steps: a number of extruded profiles (31, 32, 33, 34), each of which being defined by two edges (345, 346) and comprising a concave smooth limiting surface (341) which is located between said edges and is formed by generatrices along an arc with a radius of curvature substantially corresponding to the external diameter of the stator core, are fixed in relation to each other such that their concave limiting surfaces form a tubular configuration with a predetermined internal diameter, the number and dimension of the profiles between said edges being so chosen that, placed together around the stator core, they would essentially surround said stator core without overlapping each other and such that gaps (41, 42, 43, 44) are formed between at least some of their edges when they are fixed to said tubular configuration, and the profiles are welded together along their edges into a tubular housing by means of weld joints (51) , the width of which is adapted to fill up said gaps. 2. A method according to claim 1, characterized in that the profiles are fixed in relation to each other by being applied around an essentially cylindrical mandrel (7) with an external diameter corresponding to the predetermined internal diameter of the tubular configuration. 3. A method according to claim 1, characterized in that the profiles are applied against the mandrel by being pressed thereagainst by means of a pressure device (8) . 4. A method according to any of the preceding claims, wherein the concave limiting surface of the profiles at the edges of the profiles exhibits recesses (3411, 3412) extending along said edges, characterized in that when the profiles are welded together, a supporting bar (61) for the weld joint is placed in the recesses between two adjoining profiles.

Inventors: LOTHIAN KEITH, OLOFSSON INGEMAR, LOTHIAN, KEITH, OLOFSSON, INGEMAR
Applicants: ASEA BROWN BOVERI, LOTHIAN KEITH, OLOFSSON INGEMAR, ASEA BROWN BOVERI AB, LOTHIAN, KEITH, OLOFSSON, INGEMAR
Application year: 1994
Main classification: H02K15
IPC codes: H02K5, H02K15